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The following examples illustrate the application of this rule in rounding a few different numbers to three significant figures:
Let’s work through these rules with a few examples.
(a) 31.57 (to two significant figures)
(b) 8.1649 (to three significant figures)
(c) 0.051065 (to four significant figures)
(d) 0.90275 (to four significant figures)
(b) 8.1649 rounds “down” to 8.16 (the dropped digit, 4, is less than 5)
(c) 0.051065 rounds “down” to 0.05106 (the dropped digit is 5, and the retained digit is even)
(d) 0.90275 rounds “up” to 0.9028 (the dropped digit is 5, and the retained digit is even)
(a) 0.424 (to two significant figures)
(b) 0.0038661 (to three significant figures)
(c) 421.25 (to four significant figures)
(d) 28,683.5 (to five significant figures)
(a) 0.42; (b) 0.00387; (c) 421.2; (d) 28,684
(a) Add 1.0023 g and 4.383 g.
(b) Subtract 421.23 g from 486 g.
(a) $\begin{array}{l}\\ \begin{array}{l}\hfill \\ \frac{\begin{array}{c}\phantom{\rule{1.4em}{0ex}}\mathrm{1.0023\; g}\\ \text{+ 4.383 g}\end{array}}{\phantom{\rule{1.5em}{0ex}}\mathrm{5.3853\; g}}\hfill \end{array}\end{array}$
Answer is 5.385 g (round to the thousandths place; three decimal places)
(b) $\begin{array}{l}\begin{array}{l}\hfill \\ \hfill \end{array}\\ \frac{\begin{array}{l}\text{}\phantom{\rule{0.8em}{0ex}}\mathrm{486\; g}\hfill \\ -\mathrm{421.23\; g}\hfill \end{array}}{\phantom{\rule{1.3em}{0ex}}\mathrm{64.77\; g}}\end{array}$
Answer is 65 g (round to the ones place; no decimal places)
(b) Subtract 55.8752 m from 56.533 m.
(a) 2.64 mL; (b) 0.658 m
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